The ultimate objective of this proposal is to develop an automated chemico-enzymatic method for the synthesis of polyribonucleotides. The method will involve the stepwise addition of nucleotides to a growing polynucleotide chain using a nucleotide polymerizing enzyme with chemically-modified substrates. The chemical modifications will be chosen such that the addition of only one nucleotide unit at a time will be permitted, and this will allow the synthesis of polynucleotides of defined sequence. This approach will be exploited in the synthesis of a number of polynucleotides containing sequences of biochemical and biological interest. The synthetic method will be adapted to solid support operation and this technique will then be incorporated into a machine for the automatic production of polynucleotides of given sequence.